The application areas of two-dimensional (2D) materials, their heterostructures and composites are rapidly expanding — thanks to their extraordinary mechanical, optical, electronic and thermal properties. The family of 2D materials, which are finding a use in applications, is rapidly growing, and now includes graphene, graphene oxide, hexagonal boron nitride and transition-metal dichalcogenide, as well as the recently obtained chemical derivatives, physically modified hybrids and allotropes. New applications also trigger the development of new and more efficient methods for the synthesis of 2D materials and the formulation of composites. In this paper, we focus on the relation between the structure of the 2D materials and their heterostructures on the one hand and their properties on the other, summarize recent improvements in the synthesis approaches and discuss the perspectives in applications. We highlight existing applications in electronics, optoelectronics, electrocatalysis and energy storage and discuss new potential areas such as functional coatings and biomedical materials and devices.
The high electrical conductivity and low dimensionality of graphene is essential for the development of novel lightweight electrodes for bioenergy technologies with a zero CO2 footprint. However, the integration of graphene in ecosystems presents a formidable challenge, especially because the surface energy of graphene is not compatible with living matter. Here we propose a sustainable chemical control method to balance surface hydrophilicity and conductivity of graphene nanowalls to form a graphene-based lightweight sponge bioreactor. The few-nanometer--thick conductive nanowalls create biocompatible hydrophilic microconfinements to harvest the biomass density of electrogenic Shewanella Oneidensis MR-1. The graphene-based bioreactor shows a stable and rapid bio-current response with a steady-state bio-current density of 135.35 mA·m-2 realized within a few hours. Our novel and sustainable graphene-based material provides a revolutionarily energy opportunity for the establishment of new energy-related graphene industries as well as facilitates many startups.
A novel sulfated tin oxide solid superacid granular stacked one-dimensional (1D) hollow nanofiber (SO42-/FSnO2) is proposed as a nanofiller in sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK) to manipulate a highly conductive proton nanochannel. It has unique microstructures with an open-end hollow nanofibric morphology and grain-stacked single-layer mesoporous fiber wall, which greatly enlarge the specific surface area and aspect ratio. The diverse acid sites, that is, SO42-, Sn-OH Brönsted, and Sn4+ Lewis superacids, provide a high concentration of strong acidic proton carriers on the nanofiber surface and dynamically abundant hydrogen bonds for rapid proton transfer and interfacial interactions with -SO3H groups in the SPPESK along the 1D hollow nanofiber. As a result, long-range orientated ionic clusters are observed in the SO42-/FSnO2 incorporated membrane, leading to simultaneous enhancement of proton conductivity (226.7 mS/cm at 80 °C), mechanical stability (31.4 MPa for the hydrated membrane), fuel permeation resistance, and single-cell performance (936.5 and 147.3 mW/cm2 for H2/O2 and direct methanol fuel cells, respectively). The superior performance, as compared with that of the zero-dimensional nanoparticle-incorporated membrane, Nafion 115, and previously reported SPPESK-based membranes, suggests a great potential of elaborating superstructural 1D hollow nanofillers for highly conductive proton-exchange membranes.
The most promising way to address modern environmental and energy supply challenges is via rapid implementation of decarbonization and hydrogen production technologies. Development of gas separation membranes with high selectivity and permeability is essential for these processes. Traditional polymeric membranes often struggle to strike the right balance between these properties due to their structural and chemical limitations. Our research focuses on achieving precise control of gas diffusion pathways through on-demand regulation of material interactions in nanometer-thick composite membranes. We combine covalent organic frameworks (COFs) and graphene oxide (GO) to create COF-GO composite membranes. These materials offer enhanced gas separation performance and tailor-made selectivity. By pH-assisted self-assembly, we fine-tune material interactions, achieving a balance between selectivity and permeability by regulating the surface charge density of COF and GO. Our work presents a novel approach to gas separation by manipulating inter-layer interactions between COF and GO, paving the way for tailored gas separation. Through these efforts, we fabricate COF-GO composite membranes with controlled thickness and gas pathways. Compared to bare GO and COF membranes, the composite structure offers an optimal transport performance, enhanced selectivity in thicker membranes without losing permeability, and superior long-term stability. This enables the unique 2D transport mechanism to be utilized under real practical conditions. Our research offers a strategy for the design of composite membranes from two-dimensional (2D) materials for gas separation technologies. It contributes to sustainable decarbonization and hydrogen production solutions, bringing us closer to a greener, more environmentally friendly future.
Graphene oxide (GO) is an amphiphilic, water dispersible, chemical derivative of graphene. Widely used as a pathway to obtain graphene, it also has a number of interesting applications by itself due to its ability to form covalently and non-covalently bonded organic–inorganic hybrids and polymer composites. Thus, GO-based composites are used in numerous applications in membrane and coating technologies. It is important that due to the presence of functional acidic groups, GO possesses tunable physicochemical properties like a negatively charged polyelectrolyte and can be used as stimuli responsive membranes, membranes that can interact with environment and switch their properties on demand. Thus, ionic/molecular separation, water purification, selective sensing, and stimuli responsive properties have already been demonstrated in the laboratory. Good mechanical strength and conductivity (in its partially reduced form) make it attractive for the construction of the membranes for energy devices and sensors. However, concentration and distribution of the functional groups on GO molecules is difficult to control. It makes GO materials difficult to standardize, produce, and apply in industry. To this end, it is important to highlight recent achievement in the synthesis of GO as well as in design of GO-based energy devices, corrosion inhibiting coatings, and biomedical devices with improved working performances to evoke interest on mass production of GO with improved formulation.
Abstract Design and engineering of novel low dimensional metamaterials allow for new applications in membrane technology, aerospace and automotive industries, architecture, robotics, medicine, and textiles. Such materials can be strong, flexible, transparent, and can be assigned with different functionalities. Here, the authors explore the possibility of 2D graphene oxide (GO) surface to guide self‐assembly of 4‐cyano‐4′‐pentylbiphenyl (5CB) molecules via multiple hydrogen bonding and their clustering in optically active phases. The encapsulation of 5CB in a 2D geometry and birefringent properties of 5CB are tuned by the regulation of interaction energy between GO surface and 5CB. Chemical reduction of GO‐5CB composites results in electrically conductive reduced graphene oxide‐5CB membranes which change optical properties in response to Joule heating. The sustainable approach to the design of robust and flexible optically active materials will allow the formation of other metamaterials with different functionalities for advanced applications.
A promising way to address modern environmental and energy supply challenges is via rapid implementation of decarbonization and hydrogen production technologies. Development of gas separation membranes with high selectivity and permeability is essential for these processes but is still a bottleneck. Our research focuses on achieving precise control of gas diffusion pathways through on-demand regulation of material interactions in thin composite membranes. We combine 2D covalent organic frameworks (COFs) and graphene oxide (GO) to create COF-GO composite membranes with desirable nanosheet stacking, controllable thicknesses and pathways for gases. By pH-assisted self-assembly, we fine-tune material interactions and achieve simultaneous enhancement of permeability and selectivity by increasing membrane thickness and regulating the interactions between COF and GO nanosheets by pH. At a thickness of 1.3 μm, the COF-GO membrane, assembled under pH 4, demonstrates impressive performance in H2/CO2 equimolar mixed gas conditions (at room temperature and 1 bar), with a H2 permeability of 366 Barrer, selectivity of 15.6, and long-term stability exceeding 200 h. This work paves the way for tailored, performing gas separation with superior long-term stability. It guides the unique 2D transport mechanism to be utilized under practical conditions. Our research offers a novel strategy for the design of composite membranes from two-dimensional (2D) materials for gas separation technologies. It contributes to sustainable decarbonization and hydrogen production solutions, bringing us closer to a greener, more environmentally friendly future.
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